FIG. 1 is a block diagram showing a construction of a related-art external power control system for a portable telephone having a built-in charging function. Referring to FIG. 1, the external power control system comprises a terminal for a rechargeable battery pack 1 (hereinafter, referred to as battery power source) for operating the portable telephone, a terminal for an external power source 2 used to charge the battery-power source 1, a power key 3 of the portable telephone, a charging circuit 4 for charging the battery power source 1 by the external power source 2, a regulator 5 for receiving a voltage of the battery power source 1 or the external power source 2 at a Vin terminal and outputting a power supply voltage to the circuitry of the portable telephone via a Vout terminal, based on a logic level at an enable terminal (EN terminal), and a controller 10 for controlling the charging circuit 4 and the regulator 5.
The controller 10 comprises a charging controller 101 for controlling the charging circuit 4, a key detector 102 for detecting the depression of the power key 3, and a power maintaining unit 103 for bringing the EN terminal of the regulator 5 to a high level so as to maintain the level of the power supply voltage output from the regulator 5.
A description will now be given of the operation.
When only the battery power source 1 is connected to the portable telephone, i.e., when the external power source 2 is not connected to the portable telephone, an input voltage from the battery power source 1 is applied to the Vin terminal of the regulator 5.
In this state, the EN terminal of the regulator 5 is at a low level so that the regulator 5 does not supply the power supply voltage to the circuitry of the portable telephone via the Vout terminal.
When a user of the portable telephone depresses the power key 3, the power supply voltage is supplied to the circuitry of the portable telephone set so that the controller 10 is operated, as a result of the input voltage from the battery power source 1 being applied to the EN terminal of the regulator 5. The key detector 102 of the controller 10 detects the depression of the power key 3 and maintains the output of the power maintaining unit 103 at a high level using register access by a CPU (not shown). With this, the EN terminal of the regulator 5 is maintained at a high level. Accordingly, when the user of the portable telephone releases the power key 3, the power source maintaining unit 103 maintains the output of the regulator 5 so that power supply voltage of the portable telephone is prevented from being turned off.
The power supply voltage of the portable telephone is turned off by detecting the depression of the power key 3. The CPU uses a register access to bring the output of the power source maintaining unit 103 to a low level so that the output of the power supply to the circuitry of the portable telephone is turned off.
When the external power source 2 is connected to the portable telephone while the battery power source 1 is connected, the input voltage is applied to the Vin terminal of the regulator 5 and a voltage from the external power source 2 is applied to the EN terminal of the regulator 5. As a result, the power supply voltage is supplied from the Vout terminal of the regulator 5 to the circuitry of the portable telephone so that the controller 10 is operated.
The CPU (not shown) or an electronic circuit of the controller 10 monitors the status of the battery power source 1. By controlling the charging circuit 4 via the charging controller 101, the controller 10 operates to charge the battery power source 1 from the external power source 2. When the external power source 2 is connected to the portable telephone while the battery power source 1 is not connected, the same operation described above is performed except that the charging control is unnecessary.
In the above-described construction of the related-art external power source control system of the portable telephone, while the external power source 2 continues to supply the power to the portable telephone, the power supply voltage continues to be output via the Vout terminal of the regulator 5. Therefore, it is not possible to turn the power of the portable telephone off even when the power is no longer necessary.
When the portable telephone is used in a vehicle by using a car battery as the external power source 2, exhaustion of the car batter may be invited as a result of an electric current being wasted. When the domestic ac power source is used as the external power source 2, the user may have to incur unnecessary payment of electric bills.
The present invention has been developed in order to resolve the above-mentioned problems and has an objective of realizing an external power source control system designed to turn off, while the external power source 2 remains connected, the power supply voltage: when a charging operation is completed; when overflow of a timer, set to expire when a boost charge is completed so that the power is forced to be turned off, occurs; when a control program determines that the power need not be turned on; or when the user of the portable telephone determined that the power need not be turned on and performs required actions such as a key input and a speech input, the goals accomplished by the system being the suppression of a wasted electric current of the domestic ac power source, and reduction in electric current consumption.